Charcoal Making Methods – Small To Industrial

How To make charcoal from wood ?

Charcoal has been made by various methods since thousands years ago

The traditional of charcoal making method in Britain used a clamp. This is essentially a pile of wooden logs (e.g. seasoned oak) leaning against a chimney (logs are placed in a circle). The chimney consists of 4 wooden stakes held up by some rope. The logs are completely covered with soil and straw allowing no air to enter. It must be lit by introducing some burning fuel into the chimney; the logs burn very slowly (cold fire) and transform into charcoal in a period of 5 days’ burning. If the soil covering gets torn (cracked) by the fire, additional soil is placed on the cracks. Once the burn is complete, the chimney is plugged to prevent air from entering

old earh mount charcoal kiln

Modern charcoal making methods use a sealed metal container, as this does not require watching lest fire break through the covering.[8] However, on-site attendance is required. This is often carried out by the last forestry workers to live in working woodland in the western world. There has been a resurgence of this, particularly in the UK. A good example of this is Bulworthy Project where charcoal production supports an experiment in low-impact living and nature conservation.

The properties of the charcoal produced depend on the material charred and the charring temperature is also important. Charcoal contain varying amounts of hydrogen and oxygen as well as ash and other impurities that, together with the structure, determine the properties. The approximate composition of charcoal for gunpowders is sometimes empirically described as C7H4O. To obtain a coal with high purity, source material should be free of non-volatile compounds (sugar and a high charring temperature can be used). After charring, partial oxidation with oxygen or chlorine can reduce hydrogen levels

There are two basic methods of making charcoal: direct and indirect:

The direct method uses heat from the incomplete combustion of the organic matter, which is to become charcoal. The rate of combustion is controlled by regulating the amount of oxygen allowed into the burn and is stopped by excluding oxygen before the charcoal itself begins to burn. This is the ages old method used by colliers to make charcoal in a pit, pile (clamp) or, more recently, in metal or masonry chambers (kilns). See the links below for more information.

japanese charcoal direct method

The indirect method uses an external heat source to “cook” organic matter contained in a closed but vented airless chamber (retort). This is usually carried out in a metal or masonry chamber (furnace). The indirect method results in a higher yield of high quality charcoal with less smoke and pollutants and requires less skill and attention than the direct method.

Stage 1 drying the wood adam retort burning

On this blog we mostly write about the direct charcoal making method as a hobby . please check out my other post about related kiln and retort in small scale . if you have try yourself a good method, please share it here for everybody use .

New modern Industrial charcoal making technologies

1.1 What are industrial Charcoal Making methods?

Charcoal making is an old and honourable trade. Its origins are lost in prehistory and the traditional methods of making it have changed surprisingly little -from ancient times till now. The only new factors are that the simple methodologies have been rationalised and that science has verified the basic processes which take place during carbonisation and spelled out the quantitative and qualitative laws which govern the process.

New methods which have been introduced in some parts of the developed world have supplanted the old technology. Their newness does not reside in the principle of carbonisation itself but in the rationalisation of the use of heat, materials handling and labour and in some instances the recovery of by-products from the smoke given off during carbonisation.

These ‘industrial’ methods, for want of an easier name, in contrast to those described in (15) are certainly more complex in almost every way.

Since ‘new’ in the world of advertising is automatically assumed to mean ‘better’ it is not surprising that there has been an upsurge of interest in these new technologies by the developing world in attempting to increase the availability of charcoal and wood fuels. This Forestry Paper tries to supply a rational answer to the question:- “How can the industrial charcoal making systems make a useful contribution to charcoal production in the developing world?”

1.2 The ‘new’ and the ‘old’ in the industrial technology

If one elects to make charcoal using one or other of the methods in this paper it will still be necessary to make use of the information in (15), specially chapters 1, 4 and 9, because with the Industrial technologies about 90% of the process from the growing and harvesting of the wood to the distribution and sale of the finished charcoal is still the same as with the traditional methods. The newness resides in the carbonisation step and the replacement of labour intensive methods of materials handling with capital intensive methods.

Some of the often-claimed advantages of the industrial methods are:

– The yield of charcoal from the wood is higher.
– Carbonisation is more rapid.
– Charcoal can be made -from raw materials that cannot be processed by traditional methods.
– Industrial chemicals and heat energy can be recovered from the smoke given off during carbonisation.
– By recovering by-products from the smoke there is less pollution of the environment.

Let us take a closer look at these claims.

– The yield of charcoal is higher.

In traditional charcoal making part of the wood is burned to dry out and carbonise the remainder. During carbonisation there is also an exothermic production of heat as the wood structure decomposes to form charcoal and this supplements the heat derived from burning part of the charge. The most efficient of the retort systems described later is capable of giving yields of about one ton of charcoal from about 3.5 tons of wood providing the wood is well dried and the retort operated properly. The best that can be achieved by brick kilns is about one ton from 4.5 tons of well dried wood.

Not all industrial methods however give such high yields and most will not work properly unless the wood is well dried. Traditional methods on the other hand will operate on substantially green wood but with much lower yield.

– Carbonisation is faster.

This is a rather meaningless claim. What one really needs to know about the system are answers to such questions as ‘at what rate is charcoal produced per unit of capital invested?’ or ‘how much charcoal is produced per man year of labour employed?’ That is to say at the end of the year how much charcoal do we have for how much investment in plant and working capital?

In the developing world capital is usually scarce and labour power abundant. When it is noted that industrial methods require massive investment, usually in off-shore borrowed funds and skilled labour; industrial methods lose a lot of their glamour and obviously call for careful pre-investment studies to see where they will really lead.

– New raw materials can be carbonised.

This is certainly proved for one industrial system, the multiple hearth rotary furnace. However, it is always necessary to ask if the new material can be ‘successfully carbonised’. Many proposals have come to grief when this test has been applied. Nevertheless bark and sawdust and certain agricultural residues can be successfully carbonised now. But it is essential to ask before setting out to carbonise agricultural residues whether from all points of view this is the best use for them and if the resulting charcoal produced in the form of fine powder can be economically turned into briquettes and marketed in the particular developing country.

– Industrial chemicals can be recovered.

Most retort based industrial systems can allow the smoke given off during carbonisation to be captured and condensibles and gas recovered. The main problem in making this a success nowadays is the low price obtainable for these chemicals in relation to the high present day capital cost of setting up a recovery and refining system to process them.

– Industrial methods cause less pollution.

If the smoke from carbonisation is recovered then this source of environmental pollution is largely eliminated. This is a definite benefit where carbonisation is carried out in an urban environment. But industrial methods, especially where the smoke and fumes are captured for by-product recovery can pollute the environment in a more objectionable way. This can occur because inevitably in the process of by-product recovery, liquid effluents accumulate and have to be disposed of. If this is done carelessly then waste liquids toxic to fish and plant life escape into streams and waterways. Control of this pollution is not impossible – it just costs money.

1.3 The trade-offs in charcoal making

As in all industrial production processes, it is possible in charcoal making to trade-off part of an advantage in return for the reduction or elimination of a disadvantage.

To understand where such trade-offs may be worthwhile it is first necessary to understand clearly what the real objectives are in the charcoal making process. The first step to clearer thinking is to set-up a country-wide fuel energy policy or in this case a country-wide wood fuel energy policy which should be the framework within which all decisions of importance about charcoal making are made. The outline of how such a policy is drawn up is covered in (15) and will not be dealt with here since the main concern of this Paper is the carbonisation step and not the rest of the process which is more or less the same whatever carbonisation system is used. But the carbonisation step does reflect back and influence all other preceding stages and this has to be taken into account.

The factors which must be considered include: the yield of charcoal obtained from the wood; the capital investment required; transport economics for both the wood and charcoal; number of jobs created or lost; the relevance of attempting to recover by-products; the lift of the forest or other resource in relation to the time needed to recover the investment; the relative importance of the offshore content of loan and equity funds in the venture; and the capacity of the country to provide skilled technicians needed to operate the more complex ‘industrial’ types of charcoal making system.

1.4 Yield – Investment interactions

The most powerful decision making parameter in choosing a carbonising system for charcoal for most developing countries is the interaction between the yield of a process and the capital necessary to install it. A process which has twice the yield of a traditional one would obviously be chosen if the capital investment of both systems were the same both in amount and origin of the investment funds. But life is not usually so simple and there is normally a trade-off between yield and investment. For example if the high yield process requires substantial offshore loan funds to establish then it may be a better option in terms of local development to use locally available capital and labour to grow more wood in high yield plantations and avoid a committment to an offshore loan for a process which would probably generate far less jobs than the lower yield process. But if as is usual there is a shortage of either established forests or land on which to establish plantations then other factors being equal the capital intensive process may be attractive. Unfortunately in most developing countries which find themselves simultaneously short of land resource and foreign investment funds the decision is usually made for them and the best option they can follow is efficient use of available resources using the simple technology applied in the most efficient way. (15)

It is not proposed in this introductory note to pursue these difficult issues further but simply to emphasise strongly the need to be aware of the complexities of the situation which faces each country.

1.5 The importance of wood preparation costs

The final point requiring emphasis in this introduction is the matter of wood preparation costs.

Traditional methods are adapted to use wood in large pieces, in some of them whole tree trunks can be used. It is difficult to dry such large pieces before carbonising and so more wood is used up in the carbonising process to complete their drying before they carbonise. Thus the yield overall is lower but wood preparation costs are negligible. Industrial methods require the wood in small pieces of more or less constant size. Some retort systems even require the wood to be in the form of sawdust. Wood in smaller pieces is easier to dry in the air and hence the yield in carbonising is higher. Small dimension wood is also required for the mechanised feeding systems used in most industrial type carbonising processes. Where the wood is available already in finely divided form as sawmill waste, preparation costs are low. But in practice the amount of wood available in this form in the developing world in relation to the charcoal needed is quite small so that generally any industrial system adopted must face quite large wood preparation costs. This factor can never be disregarded.